The present invention relates to a line length measuring device for a fishing reel employing an ultrasonic sensor.
To improve the angling, in recent years, most fishing reels are equipped with a line length measuring device as disclosed in JP-A-5-23082, in which the line length measuring device measures the amount of delivering the fishline or the amount of winding the line to allow a contrivance to be let out at a predetermined shelf position.
The line length measuring device has an ultrasonic sensor for transmission and an ultrasonic sensor for reception that are mounted on a reel main body in almost V-character shape to a spool face of a spool, in which the spool diameter data is obtained on the basis of the time for which an ultrasonic wave radiated by the ultrasonic sensor for transmission onto the spool face of the spool is received by the ultrasonic sensor for reception, the line length is measured and calculated in accordance with the spool diameter data and the number of rotations of the spool detected by rotational number detecting means, and the measured value is displayed on a display screen of an operation panel.
However, due to a property of fluctuating with the sound wave, the ultrasonic wave is affected under the service environment of the ultrasonic sensor, and the velocity of ultrasonic wave is varied along with the temperature.
Since the line length measuring device did not take into consideration the change in the velocity of ultrasonic wave due to environmental variations on the fishing spot, there was the risk that the line length could not be measured correctly even with a slight error due to a temperature change.
Thus, the present applicant has made improvements on the line length measuring device as described in JP-A-7-39284, and has proposed the line length measuring device in which an error in line length measurement due to a temperature change is resolved.
This line length measuring device has a temperature sensor for sensing the ambient temperature around the fishing reel mounted on the reel main body, and from the ambient temperature Txc2x0 C. sensed by the temperature sensor, the velocity of ultrasonic wave is calculated in accordance with the following calculation expression
Velocity=(331.5+0.61T)m/sec 
in which this calculated velocity of ultrasonic wave is used for measuring the line length. With the line length measuring device, the line length measurement is enabled at high accuracy by means of the ultrasonic sensor without being affected by the environmental variations around the fishing spot through all the seasons.
However, the line length measuring device, like that as disclosed in JP-A-5-23082, has two ultrasonic sensors for transmission and reception on the reel main body, and further requires a temperature sensor to be mounted on the reel main body, in addition to the ultrasonic sensor, so that the entire reel is increased in size and weight due to a mounting space, and the number of parts is increased, leaving the problems with a complicated structure, and higher manufacturing costs.
The present invention has been achieved in the light of the above-mentioned problems, and it is an object of the invention to provide a line length measuring device for fishing reel that can measure the line length at high accuracy by means of an ultrasonic sensor without being affected by environmental changes of the fishing spot, while reducing the entire reel in size and weight and simplifying the structure with lower costs.
In order to accomplish the above object, according to an aspect of the present invention, there is provided a line length measuring device for a fishing reel that measures and displays the line length from the spool diameter data and the number of rotations of a spool detected by rotational number detecting means by acquiring the spool diameter data on the basis of the time for which an ultrasonic wave is radiated from an ultrasonic sensor mounted on a reel main body onto a spool face of the spool and its reflected wave is received by the ultrasonic sensor, characterized by comprising velocity measuring means for detecting a velocity of ultrasonic wave radiated from the ultrasonic sensor, in which the spool diameter data is acquired on the basis of the velocity of ultrasonic wave measured by the velocity measuring means.
According to another aspect of the invention, there is provided the line length measuring device for the fishing reel, characterized in that the fishing reel comprises a single ultrasonic sensor, a spool direction reflection portion for reflecting an ultrasonic wave radiated from the ultrasonic sensor onto the spool face of the spool, and a direct reflection portion for directly reflecting the ultrasonic wave radiated from the ultrasonic sensor onto the ultrasonic sensor, wherein velocity measuring means calculates the velocity of ultrasonic wave on the basis of the time for which the ultrasonic wave is reflected from the direct reflection portion and its reflected wave is received by the ultrasonic sensor.
The line length measuring device according to one aspect of the invention obtains the line length from the spool diameter data and the number of rotations of the spool detected by rotational number detecting means by acquiring the spool diameter data on the basis of the time for which an ultrasonic wave is radiated from an ultrasonic sensor onto the spool face of the spool and its reflected wave is received by the ultrasonic sensor, in which in measuring the line length, the spool diameter data is based on the velocity of ultrasonic wave measured by velocity measuring means.
The line length measuring device according to another aspect of the invention obtains the line length from the spool diameter data and the number of rotations of the spool detected by rotational number detecting means by acquiring the spool diameter data on the basis of the time for which an ultrasonic wave is radiated from the ultrasonic sensor onto the spool face of the spool direction reflection portion and its reflected wave is received by the ultrasonic sensor, in which in measuring the line length, velocity measuring means calculates the velocity of ultrasonic wave on the basis of the time for which the ultrasonic wave is reflected from the direct reflection portion and its reflected wave is received by the ultrasonic sensor.
The present disclosure relates to the subject matter contained in Japanese patent application No. 2000-190535 (filed on Jun. 26, 2000), which is expressly incorporated herein by reference in its entirety.